Particle Shutdown of Radiatively Driven Convection

Radiation can drive natural convection in a shallow fluid layer, such as the near-shore region of lakes or shallow ponds. If the radiation is from above, as it travels through the layer, it is absorbed by the fluid, heating up the top of the layer and creating a stable thermal stratification. If the layer is sufficiently shallow, some radiation reaches the bottom of the layer and is absorbed by the bottom boundary. The boundary will heat up and re-emit the absorbed energy back into the fluid as a heat flux. This heat flux can drive natural convection in the layer. This system has been recently examined experimentally.

If the fluid layer contains particles that are negatively buoyant, these will initially sit on the bottom of the layer. If the radiatively-driven convection is sufficiently strong, then these particles are lifted up into the bulk of the flow. If the particles can absorb radiation, then they will change the mean absorption properties of the flow, absorbing more of the radiation as it travels through the layer, potentially stabilising the flow. If the flow is stabilised, then the negatively buoyant particles will settle to the bottom, potentially starting a cyclical process of convection and stabilisation.

This project will perform laboratory experiments to identify what occurs in a shallow fluid layer, forced by radiation from above and containing dark, negatively buoyant particles. The buoyancy of the particles can be varied by changing the density of the fluid (using salt) and the depth of the fluid layer can be varied.